I've purchased 3 Olimexino-GD32 boards from Amazon and after 10-20 uploads, for every single one of them I can no longer upload via native USB port. Essentially my Mac OS X stopped recognizing the boards. The weird thing is that the last uploaded sketch was still running fine, so I'm guessing the MCU is fine (at least that part).

Any ideas why this is the case?

Thanks!

Rhodos:
Quick update: I successfully restored the bootloader via Serial and ST Flash Loader. Everything works right now, but I'm concerned the bootloader will get corrupted again somehow (I still do not understand what happened). Anyway, without this glitch, the GD32 is quite a bit faster than the STM32.